I recently bought a 5/8 size double bass which was made in Mexico(I live 3 mile from the border). I would like to replace the nut-can anyone tell me how to do this myself?

Not to be facetious or anything, but get a hunk of ebony and carve away everything that doesn't look like a bass nut. ;-)

I usually use a scroll saw and then a dremel with a sanding cylinder to shape it, then various sandpaper grades to make it pretty.

Really -- that's all there is to it.